1. Field of the Invention
The present invention relates to a process for the carboxylation of ethylene-vinyl acetate copolymers or saponified copolymers. More particularly, the present invention relates to a process in which carboxylic acid residues are incorporated into an ethylene-vinly acetate copolymer or saponified copolymer thereof such that the resultant product maintains the physical form of the original copolymer such as the powdered or pelletized form of the copolymer.
2. Description of the Prior Art
Various attempts have been made to introduce carboxylic acid residues into ethylenic polymers such as ethylene-vinyl acetate copolymers in order to substantially improve the bonding characteristics of the copolymers without deterioration of the excellent properties of the ethylene-vinyl acetate copolymers such as softness, melt flowability, toughness and adhesion. Such a chemical modification has been performed on ethylene-vinyl acetate copolymers by a method in which the reaction is conducted in the molten state and by a method in which the polymer is dissolved in a solvent and the reaction is performed in solution. No method is known in which the reaction can be conducted conveniently while maintaining the original form of the polymer, for example, as a powdered or pelletized material.
If carboxylation of a copolymer can be accomplished by a heterogeneous reaction in which the original powdered or pelletized form of the polymer is retained, such complicated steps which are inherent in the conventional solution method, as dissolution of the polymer before the reaction, separation of the carboxylated polymer and pelletization of the separated polymer, will become unnecessary. Such a method would have industrial advantages.